Journal of Nannop1ankton Research, 19, I, 1997.

MJ Sty zen:Cascading counts of nannofoss il abundance, p. 49 .

CASCADING COUNTS OF NANNOFOSSIL ABUNDANCE
Michae/J. Styzen, Shell Offshore Inc., PO Box 61933. New Orleans, LA 70161 . USA

Introduction

Ex1ra Abundant (XA) .. ...... ........... .. ...... ..... ............. 2001-9999
Extra Extra Abw1dant (XXA) .. .... ....................... ... >9999

The following article has been posted on the ' coccolith.list'on a couple of occasions. It was originally written at therequest ofBrian O ' Neill , my boss, so he could distribute itto the Industry Coordinators group. Since it was posted, I
have received several positive responses from folks who
have modified it to their own uses. On at least one occasion it has been cited as a personal communication. Since
it has proved to be so useful, it was decided that it would
be best to publish it.

Procedure
To use the cascading counting method, one moves fromone whole fov to the next for a full traverse across thewidth of the coverslip. During the first quarter-traverse,
one counts the number of fov examined. The number ofindividuals for each taxon are counted until 10 fov areexamined. At this point, the number of individuals in any
taxon with a double digit or greater count is multiplied by
12 (to relate to the full traverse) and the corresponding
relative abundance is assigned.
At 15 fov, any double-digit count of the remaining
taxa is multiplied by 8 to get a relative abundance. This
procedure is repeated until the quarter-traverse is completed. After a quarter-traverse, all but the taxa with thelowest abundances have been assigned a relative abundance. At tltis point, the remaining taxa can be counted forthe rest of the traverse witl10ut accumulating unduly highcounts. ,In exceptionally rich samples, the cascade can bestarted at a lower number offov (taxa in the higher abundance categories can usually be estimated from one or twofov). Relative abundances obtained using this method,when compared with counts of a full traverse, have beenfound to be extremely accurate.

Methodology
Statistical data for nannofossils is usually obtained bycounting individuals of each taxon in a very limited numberof fields of view (sometimes as low as 5-10). We havefound that such a small sample-size yields unreliable results, especially in sparser samples. Using the following
procedure, all statistics are based on the number of individuals of a given taxon observed in a full traverse comprising 120 250f..Lm fields of view (fov). A cascading counting method is used to achieve a statistically significant
sampling without being overly time-consuming.
The abundance categories are as follows :Rare(R) ... ................ ............ ... .... ..... .............. ....... .. .. 1-5
RaretoFrequent(RF) .... .. .. ....... .. ..... ..... .. ........ ... .. .. 6-15
Frequent(F) ... .. ....... ..... ... ..... .. .. .. ..... ..... ... .... ... .. ..... ... 16-35
Frequent to Common (FC) ...... .. .... .... ......... ... .... ..... 36-75
Common(C) .. ... ... ........ ............ ..... ... .......... ....... ..... ... 76-150
Common to Abundant (CA) ............ .. ................... 51-300
Abundant (A) ........ ............... .. ..... ... .. .... ... .... ... ........ 301-600
Very Abundant (VA) .. .......... ........ ...... .... ... ............. 601-1000
Very Very Abundant (VVA) ................ .................. 1001-2000

This takes longer to explain than to put into practice!
Equipment used: nticroscope - Zeiss Axioscope; objective- x63 Ph3 Planapochromat; oculars - xl6. Slides are prepared with polymer-treated samples, 30mm coverslip affixed with Pyccolyte.

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